1. Field of the Invention
The invention relates in general to a television signal receiving device and a method for determining whether a channel includes a television program signal, and more particularly to a device and a method capable of quickly determining whether a channel includes a television program signal for an Integrated Services Digital Broadcasting-Terrestrial (ISDB-T) television system or a Digital Video Broadcasting-Terrestrial (DVB-T) television system.
2. Description of the Related Art
One function of a television receiver is scanning television channels, i.e., determining whether a specific television channel includes a television program signal. FIG. 1 shows a functional block diagram of a conventional Integrated Services Digital Broadcasting-Terrestrial (ISDB-T) signal receiver. In digital television broadcasting, a radio-frequency (RF) signal includes multiple television channels, each of which including more than one television program signals. After receiving the RF signal from an antenna 105, a tuner 110 selects a target channel from the multiple channels, and down-converts the RF signal in the target channel to an intermediate low frequency signal. The target channel is inspected by a subsequent circuit whether it includes the television program signal. An analog-to-digital converter (ADC) 115, coupled to the tuner 110, converts an analog signal carried in the target channel to a digital signal. A fast Fourier transform (FFT) circuit 125 converts the digital signal from the time domain to the frequency domain, and includes synchronization circuits at its front and rear ends. As the two synchronization circuits respectively process the synchronization procedure of the digital signal in the time domain and the frequency domain, they are respectively named as a time-domain synchronization circuit 120 and a frequency-domain synchronization circuit 130. The time-domain synchronization circuit 120 is coupled to the ADC 115. Since the time-domain synchronization circuit 120 and the frequency-domain synchronization circuit 130 are respectively located and front and rear ends of the FFT circuit 125, the two may also respectively be referred to as a pre-FFT synchronization circuit and a post-FFT synchronization circuit.
The time-domain synchronization circuit 120 analyzes and obtains required synchronization information of signals in the time domain; the frequency-domain synchronization circuit 130 analyzes and obtains required synchronization information of signals in the frequency domain. In practice, it may be regarded that the time-domain synchronization circuit 120 processes a coarse-tune step of the synchronization procedure of the digital signal, and the frequency-domain synchronization circuit 130 processes a fine-tune step of the synchronization procedure for the digital signal. The synchronization procedure that the frequency-domain synchronization circuit 130 handles for the digital signal includes a correlation operation to obtain a plurality of correlation values, according to which a carrier frequency offset (CFO) of the digital signal can be determined. More specifically, the CFO may include an integer carrier frequency offset (ICFO) and a fractional carrier frequency offset (FCFO), and the correlation values may be further categorized into ICFO correlation values and FCFO correlation values. As shown in FIG. 1, the frequency-domain synchronization circuit 130 is directly coupled to the time-domain synchronization circuit 120, in the aim of transmitting ICFO information to the time-domain synchronization circuit 120. Thus, the time-domain synchronization circuit 120 may compensate the digital signal according to the ICFO correlation values such that the frequency offset no longer exists in the compensated signal.
Again referring to FIG. 1, a channel estimation circuit 135 is coupled to the frequency-domain synchronization circuit 130, and mainly serves for estimating a multipath interference of the digital signal. An equalizer 140 is coupled to the channel estimation circuit 135, and mainly serves for filtering out signals of channels other than a main channel according to an estimation result of the channel estimation circuit 135. A transmission and multiplexing configuration control (TMCC) decoding circuit 145 is coupled to the equalizer 140, and analyzes and obtains information such as a modulation mechanism and a code rate of inner code of the digital signal. The TMCC decoding circuit 145 is sequentially coupled to a frequency-domain deinterlacing circuit 150 and a time-domain deinterlacing circuit 155, which respectively deinterlace the digital signal in the frequency domain and in the time domain. A quadrature amplitude modulation (QAM) demapping circuit 160 is coupled to the time-domain deinterlacing circuit 155, and demodulates the digital signal. Circuits coupled subsequent to the QAM demapping circuit are sequentially coupled an internal deinterlacing circuit 165, a Viterbi decoder 170 and an external deinterlacing circuit 175. The internal deinterlacing circuit 165 and the external deinterlacing circuit 175 internally and externally deinterlace the digital signal, respectively. The Viterbi decoder 170 performs Viterbi decoding on the digital signal. Eventually a Reed-Solomon decoding circuit 180, coupled to the external deinterlacing circuit 175, performs Reed-Solomon decoding on the digital signal to generate a transport stream signal required by the television system.
In the prior art, it can be learned whether a target channel includes a program signal usually only after the Reed-Solomon decoding circuit 180 completes the corresponding decoding process. In some publications, it is proposed that information such as the foregoing modulation mechanism and code rate of inner rate be utilized to bring forward the time point for determining whether the target channel includes a television program signal. However, as the average time needed for such determination process is about 300 ms to 550 ms, the total time required for scanning all channels adds up to a substantial amount for a large number of channels.